1. Field of Invention
This invention relates generally to video monitors and automatic alignment systems for video monitors, particularly automatic alignment systems including circuits for adjusting or correcting predetermined characteristics of the monitor's displayed image during the horizontal scan of the monitor.
2. Description of the Background
Video monitors, such as for use with digital computers, typically include a cathode ray tube (CRT) and driver circuitry including video, horizontal and vertical amplifiers. Early versions of video monitors included a variety of potentiometers which were adjusted at the factory to align and adjust the display presented on the CRT. Also, a few pots were accessible on the exterior of the monitor for adjustment by the user. The external pots commonly included controls for brightness, contrast and possibly horizontal and vertical size and center position.
More modern monitors often include a relatively larger number of adjustable parameters which can be used to provide a more precisely-aligned and color-balanced display. Some of the modern monitors include digital control circuits for storing values of these adjustable parameters and for controlling the driver circuitry of the monitor in accordance with the stored values.
U.S. Pat. No. 5,216,504 for "Automatic Precision Video Monitor Alignment System" is specifically incorporated herein by reference for all that it discloses. This patent discloses an alignment system including a pick-up camera located adjacent to the CRT of a monitor for capturing an image of the display and communicating the image to a computer. The computer communicates with a microprocessor and digital control circuit within the monitor which control the video driver circuit of the monitor. The system operates to automatically and optimally adjust the alignment and color balance of the display for the particular video signal which is applied to the monitor and for the particular settings of the external controls on the monitor.
In order to most accurately adjust the alignment and color balance of the display, it is desirable to make variable adjustments during the vertical and horizontal scan of the CRT by the driver circuitry. Variable adjustments during the vertical scan of the CRT by the driver circuitry accomplished by a voltage waveform generator which develops a pulse-width modulated (PWM) signal for each display parameter to be controlled. As disclosed in U.S. Pat. No. 5,216,504, the width of the PWM signal corresponds to the magnitude of the target value for the display parameter. The pulse-width can be varied during the vertical scan to give the desired target value. Rather than provide a separate PWM signal for each horizontal line in the vertical scan, the lines are grouped into a smaller number of segments. A separate PWM signal is provided for each segment, with each signal representing the rate of change of the display parameter during the given segment. This rate of change is integrated once to form a smooth correction.
Unfortunately, no such correction is available for variable adjustment during the horizontal scan of the CRT due to the much higher horizontal scan frequency versus the vertical scan frequency.
It is against the background, and the limitations and problems associated therewith, that the present invention has been developed.